Copper(I) Acetate‐Catalyzed Cycloaddition between Azomethine Imines and Propiolates under Additive‐Free Conditions

Abstract

Because propiolates easily undergo base‐catalyzed self‐Michael addition, most popular catalytic systems in CuAAC cannot be used in the cycloaddition between azomethine imines and propiolates, because such reactions usually require the use of tertiary amines as additives (as base and/or ligand). We found that this problem can be resolved simply by using copper(I) acetate as catalyst, in which the acetate serves as a ligand and is converted into acetic acid during the reaction. Thus, copper(I) acetate catalyzed cycloaddition actually proceeds under additive‐free conditions (without exogenous ligand) to efficiently give 6,7‐dihydropyrazolo[1,2‐a]pyrazolone derivatives, in which the side‐reactions and byproducts caused by basic additives are completely avoided.

A highly efficient [3+2] cycloaddition of nitrile oxides and azomethine imines to N-vinylpyrroles

“…1 H, 13 C NMR spectra of new compounds. Supplementary data associated with this article can be found in the online version, at doi: M A N U S C R I P T A C C E P T E D …”

Solvent-free 1,3-dipolar cycloaddition of azomethine imines with terminal alkynes promoted by calcium fluoride under the ball milling condition

“…We also tested Al 2 O 3 and celite as different grinding aid in optimization condition, and the yields of 75% and 81% are obtained, respectively, which is lower than the yield of 90% when SiO 2 was used. A possible reaction mechanism to explain the formation of products 3 follows the commonly accepted pathway [19][20][21][22][23] . The copper acetylide is probably produced from cuprous acetate in the present of calcium fluoride, and the displaced hydrogen combines with acetate to provide an acidic environment(step i in Scheme 1).…”

“…[17][18][19]23], a stirred solution of hydrazinium hydrate(1 mL, 20.5 mmol) and methyl acrylate(2 mL, 22.5 mmol) in EtOH(20 mL) was heated at 70 °C for 4 h. EtOH was then removed in vacuum, and the residue was diluted with MeOH(5 mL) and benzaldehyde(3 mL, 30.7 mmol). The mixture was stirred for 10 h at room temperature and then diluted by Et 2 O(25 mL).…”

“…In 2003, Fu and co-workers [17,18] reported the enantioselective 1,3-dipolar cycloaddition of azomethine imines with terminal alkynes in the presence of copper(I) salts and ligands for the first time. Afterwards, several copper-catalyzed 1,3-dipolar cycloadditions of azomethine imines with alkynes were reported by other researchers [19][20][21][22][23][24] . However, all of these systems involved organic solvents, such as toluene, THF and dichloromethane, which inspired us to develop a solvent-free procedure for the synthesis of N,N-bicyclic pyrazolidinone derivatives.…”

Synthesis and Photo- and Ionochromic and Spectral-Luminescent Properties of 5-Phenylpyrazolidin-3-one Azomethine Imines

“…To a lesser extent, the compounds with negative photochromism [10]-norbornadienes [11,12], acylotropic enaminoketones [13], and azomethine imines [14]-are described. Azomethine imine molecules possess a polar 1,3-dipole N − -N + =C fragment, which makes these compounds to be valuable precursors in the combinatorial chemistry of heterocycles prepared by cycloaddition reactions [15][16][17][18][19][20][21]. The resulting products containing a pyrazolidine cycle annulated to other heterocycles find application in medicine as the multipurpose biologically active compounds [22], anti-HIV agents, inhibitors of NO synthase, and antidiabetic drugs [23][24][25][26], in agriculture [27,28], and in other fields of science and technology [29].…”